The trend of development in semiconductor elements nowadays is toward smaller line width and higher integrated density. When the minimum line width of an integrated circuit is reduced to below 0.25 μm, the time delay (RC delay) caused by the resistance of the metal wire itself and the spurious capacitance of the dielectric layer becomes a crucial influence on the operation rate of the elements. Therefore, in order to increase the operation rate of the elements, copper metal wires have been gradually adopted in high-level processing below 0.13 μm to replace the traditional aluminum-copper alloy wires.
The application of chemical mechanical planarization technology in the copper metal wire processing not only overcomes the problem of difficulty in defining patterns due to the difficulty of copper metal etching, but also forms a plane with global planarity upon polishing, so that the multilayer wire processing can be easily carried out. The principle of chemical mechanical planarization is that wear is produced on the wafer surface by utilizing both polishing particles and chemical aids in a polishing slurry, whereby the higher part of the uneven surface has a high removal rate due to high pressure while the lower part of the uneven surface has a low removal rate due to low pressure, and thus the purpose of global planarity can be achieved.
Large quantities of fine polishing particles and chemical aids in the polishing slurry and the scraps peeled during the wafer polishing may attach to the wafer surface during the polishing step of the chemical mechanical planarization. In general, the common contaminants found on the chips after polishing are metal ions, organic compounds, polishing particles, and the like. If there is no effective cleaning procedure to remove the above-described contaminants, the subsequent processing will be affected, and the yield and the reliability of the elements will decrease. Therefore, the cleaning processing during or after the CMP polishing has become a crucial technology to determine whether CMP can be successfully applied in semiconductor processing.
In the polishing slurry used in copper processing, benzotriazole (BTA) and its derivatives are often employed as a corrosion inhibitor. In the contaminants generated by polishing wafers in the copper processing, the organic BTA residues are most difficult to remove, mainly because the BTA residues are bonded on the copper wires by chemical adsorption. Physical removal methods such as static repulsive force, ultrasonic vibration, scrubbing with a polyvinyl alcohol (PVA) brush etc., are traditionally used, but it is not easy to obtain a good cleaning effect.
Traditional inter-metal dielectric layers and W plugs that have been treated by chemical mechanical planarization are usually cleaned with ammonia solution and/or fluorine-containing compounds, but the above solutions are not suitable for the wafers for copper metal wires. The ammonia solution will unevenly corrode the surface of copper metal, resulting in coarsening. The fluorine-containing compounds will not only coarsen the copper surface but also cost more in terms of human safety protection and waste solution treatment in order to avoid doing harm to human health and to the environment.
Ina et al. disclose in U.S. Pat. No. 6,139,763 a polishing composition that can effectively remove tantalum metal from a substrate, which consists of polishing particles, an oxidant that can oxidize tantalum metal, a reducer that can reduce tantalum oxide (such as oxalic acid) and water. This polishing composition can further comprise piperazine (a nitrogen-containing heterocyclic organic base). According to Ina et al.'s teaching, the piperazine can be used on the surface of the copper layer during polishing to prevent the formation of surface impairment, such as recesses, dishing or erosion, which also can protect the polishing surface so as to produce a mirror-like surface. However, the use of the piperazine in an aqueous cleaning solution employed in the post chemical mechanical planarization in the copper processing is not taught or suggested by Ina et al.
Small discloses in U.S. Pat. No. 6,546,939 (Taiwan Patent No. 396202) a method of removing chemical residues from a surface of a metal or dielectric layer, wherein an aqueous composition with a pH between 3.5 and 7 is placed in contact with the metal or dielectric layer for a period of time sufficient to remove the chemical residues. This aqueous composition comprises an organic acid having mono-, bi- or trifunctional groups, a buffering amount of a base of quaternary amine, ammonium hydroxide, hydroxylamine, hydroxylamine salt or hydrazine salt, and a choline hydroxide.
Small et al. disclose in U.S. Pat. No. 6,498,131 a cleaning agent. The cleaning agent consists of a nonionic surfactant, amines, quaternary amines and a surface retention agent selected from ethylene glycol, propylene glycol, polyethylene oxide and mixtures thereof, and is used to clean the residues of the chemical mechanical planarization processing.
Naghshineh et al. disclose in U.S. Pat. No. 6,492,308 a cleaning agent. The cleaning agent consists of tetraalkylammonium hydroxide, polar organic amine and a corrosion inhibitor, and is used to clean a copper-containing integrated circuit.
Nam discloses in U.S. Pat. No. 5,863,344 a cleaning agent. The cleaning agent consists of tetramethylammonium hydroxide, acetic acid and water, and is used to clean semiconductor elements, wherein the volume ratio of acetic acid to tetramethylammonium hydroxide is preferably 1 to about 50.
Masahiko et al. disclose in U.S. Pat. No. 6,716,803 a method of cleaning a semiconductor substrate with copper wires on its surface. The cleaning agent used in this method comprises a surfactant and a nitrogen-containing alkaline substance.
Ward et al. disclose in U.S. Pat. No. 5,988,186 a cleaning agent. The cleaning agent consists of a water-soluble polar solvent, an organic amine and a benzene ring corrosion inhibitor, and is used to remove organic and inorganic substances.
Walker et al. disclose in U.S. Patent Publication No. 20060229221 (Taiwan Publication No. 200706647) a liquid cleaning agent providing a low metal etching rate. The cleaning agent consists of a quaternary ammonium hydroxide, an alkyl alcohol amine, and water, and is used for cleaning microelectronic substrates.
Chen et al. disclose in U.S. Patent Publication No. 20070066508 (Taiwan Publication No. 200641121) an aqueous cleaning composition for semiconductor copper. The cleaning composition comprises a nitrogen-containing heterocyclic organic base, an alcohol amine, and water, and is used for cleaning wafers having copper wires that have been treated by chemical mechanical planarization in integrated circuit processing.
With the development of semiconductor wafer processes, the width between the metal wires has been reduced to 32 nanometers. There remain many problems associated with the new planarization processes to be solved. For instance, the surface roughness of the wafer surfaces with nano line widths that have been processed may become poor, and the properties of copper wire wafers with a reduced line width, as measured by an open/short test and reliability test, may also become poor. For cleaning processes for wafers having copper circuits, there is a need for cleaning compositions that can more effectively remove the contaminants from the surfaces of the wafers and reduce the defects on the wafer surfaces than the prior art.